<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>mydemo</title>
	<style type="text/css">
		body,div,input {margin:0;padding:0;}
		input {outline:none;}
		#outer {width:300px;margin:10px auto;padding:0 15px 30px;color:white;background:black;text-align:center;}
		#outer input.f-text {width:35px;height:20px;margin:30px 5px;text-align:center;}
		#btn {display:block;width:270px;margin:0 auto;background:green;padding:10px;text-align:center;color:white;font-size:20px;cursor:pointer;}

	</style>
	<script type="text/javascript">
		window.onload = function() {
			var oDiv = document.getElementById("outer");
			var oBtn = document.getElementById("btn");
			var s = false;
			var timer = null;/*空值？？？？*/
			oBtn.onclick = function() {
				if (s==false) {
					timer = setInterval(updateTime,1000);
					updateTime();

					this.style.cssText = "background:red";
					this.innerHTML = "取消";
					s=true;
				}
				else {
					clearInterval(timer);

					this.style.cssText = "";
					this.innerHTML = "启动";
					s=false;
				}
				function format(a) {
					return a.toString().replace(/^(\d)$/,"0$1");
				}
				function updateTime() {
					var oInput = oDiv.getElementsByTagName("input");
					/* 分钟位的数转为秒数，加上秒位的数 */
					var oRemain = oInput[0].value.replace(/^0/,"")*60 + parseInt(oInput[1].value.replace(/^0/,""));
					/* 当分秒全部归零时，清除重复*/
					if (oRemain <= 0) {
						clearInterval(timer);
						return;
					}
					/* 自动减一运算 */
					oRemain--;
					/* 分秒位重新赋值 */
					oInput[0].value = format(parseInt(oRemain / 60));
					oRemain %= 60;
					oInput[1].value = format(parseInt(oRemain));
				}
			}
		}
	</script>
</head>
<body>
	<div id="outer">
		<input type="text" class="f-text" readonly="readonly" maxlength="2" value="01"/>
		<span>分钟</span>
		<input type="text" class="f-text" readonly="readonly" maxlength="2" value="10"/>
		<span>秒</span>
		<button id="btn">启动</button>
	</div>
</body>
</html>